Pallet based system for forming thin-film solar cells

ABSTRACT

The present invention provides a photovoltaic thin-film solar cell produced by a providing a pallet based substrate to a series of reaction chambers layers can be sequentially formed on the pallet based substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/626,843, filed Nov. 10, 2004.

FIELD OF THE INVENTION

The invention disclosed herein relates generally to the field ofphotovoltaics and more specifically to the product and method ofmanufacturing thin-film solar cells using a pallet based system toprevent the formation of defects during deposition.

BACKGROUND OF THE INVENTION

The benefits of renewable energy are not fully reflected in the marketprice. While alternative energy sources such as photovoltaic (PV) cellsoffer clean, reliable, and renewable energy, high product costs and lackof production reliability have kept these devices from being a viablecommercial product. With the demand for energy going up, the worlddemand for alternatives to present energy sources is increasing.

Although relatively efficient thin-film PV cells can be manufactured inthe laboratory, it has proven difficult to commercially scalemanufacturing processes with the consistent repeatability and efficiencycritical for commercial viability. Moreover, the cost associated withmanufacturing is an important factor preventing the broadercommercialization of thin-film solar cells. The lack of an efficientthin-film manufacturing process has contributed to the failure of PVcells to effectively replace alternate energy sources in the market.

Thin-film PV cells can be manufactured according to varied designs. In athin-film PV cell, a thin semiconductor layer of PV materials isdeposited on a supporting layer such as glass, metal, or plastic foil.Since thin-film materials have higher light absorptivity thancrystalline materials, thin-film PV materials are deposited in extremelythin consecutive layers of atoms, molecules, or ions. The typical activearea of thin-film PV cells is only a few micrometers thick. The basicphotovoltaic stack design exemplifies the typical structure of a PVcell. In that design, the thin-film solar cell comprises a substrate, abarrier layer, a back contact layer, a mixed type semiconductor sourcelayer, an absorber layer, an n-type junction buffer layer, an intrinsictransparent oxide layer, and a conductive transparent oxide layer.Compounds of copper indium gallium diselenide (CIGS) have the mostpromise for use in absorber layers in thin-film cells and fit within theclassification of copper-indium selenium class, called CIS materials.CIGS films are typically deposited by vacuum-based techniques.

Thin-film manufacturing processes suffer from low yield due to defectsin the product that occur during the course of deposition. Specifically,these defects are caused by contamination occurring during processingand materials handling, and the breakage of glass, metal, or plasticsubstrates. Thus, a process for manufacturing thin-film solar cells thatboth limits potential contamination during processing and concurrentlyminimizes substrate breakage is desired in the art.

Currently, cells are manufactured using a multi-step batch processwherein each product piece is transferred between reaction steps. Thistransfer is bulky and requires the reaction in chambers to be cycled. Atypical process consists of a series of individual batch processingchambers, each specifically designed for the formation of various layersin the cell. Problematically, the substrate is transferred from vacuumto air—and back again—several times. Such vacuum breaks may result incontamination of the product. Thus, a process that minimizes vacuumbreaks is desired in the art.

While an alternate system uses a series of individual batch processingchambers coupled with a roll-to-roll continuous process for eachchamber, the discontinuity of the system and the need to break vacuumcontinues to be a major drawback. Additionally, the roll-to-roll processmay impose flexing stress on substrates, resulting in fracturing andbreakage. Such defects compromise layer cohesiveness and may result in azero yield.

Also contributing to the low yield in PV cell manufacturing is therequirement of high-temperature deposition processes. High temperaturesare generally incompatible with all presently known flexible polyimideor other polymer substrate materials.

For example, U.S. Patent Application 2004/0063320, published by Hollarson Apr. 1, 2004, discloses a general methodology for continuouslyproducing photovoltaic stacks using a roll-to-roll system. As discussedabove, this process requires the application of flexing stress to thesubstrate. This stress potentially results in fractures and breakage.Fractures or breakage reduce high quality stack structures and lowermanufacturing yield. Thus, to be a commercially viable process, thedisclosed system requires a flexible substrate for the production of thestack. However, no currently known flexible polymer materials canwithstand the high-temperature deposition process. Therefore, a processthat does not impose flexing stress on the substrates, where thesubstrates can withstand the high-temperature deposition process, isdesired in the art. So a process for manufacturing PV work pieceseffectively, and capable of large scale production are needed.

SUMMARY OF THE INVENTION

The present invention provides a photovoltaic device produced byproviding a pallet-based substrate to a series of reaction chamberswhere sequentially a barrier layer, a back contact layer, asemiconductor layer or layers, alkali materials, an n-type junctionbuffer layer, an intrinsic transparent oxide layer, a transparentconducting oxide layer and a top metal grid can be formed on the pallet.

A method is further disclosed for forming a photovoltaic device in acontinuous fashion by employing a train of the pallet based holdersloaded with work pieces. In this embodiment, a series of pallets arepassed at a defined rate through a reactor having a plurality ofprocessing zones, wherein each zone is dedicated to one production stepstage of device manufacture.

These production steps may include: a load or isolation zone forsubstrate preparation; environments for depositing a barrier layer, aback contact layer, semiconductor layer or layer and alkali materials;an environment for the thermal treatment of one or more of the previouslayers; and an environment for the deposition of: an n-type compoundsemiconductor wherein this layer serves as a junction buffer layer, anintrinsic transparent oxide layer, and a conducting transparent oxidelayer. In a further embodiment, the process may be adjusted to comprisegreater or fewer zones in order to fabricate a thin film solar cellhaving more or fewer layers.

A pallet type system may be employed where a plurality of work piecesare held as a pallet and a plurality of pallets are processed though acontinuous reactor step apparatus. This pallet based system allowscontinuous processing of smaller work pieces and alternative materialshandling steps, such as pallet stacking in intermediate or final steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a thin-film solar cell produced by theproduction technology of the present invention.

FIG. 2 schematically represents a reactor for forming solar cells.

FIG. 3 shows a plurality of work piece substrates on a device capable ofaffixing the substrates onto a carrier that also has means that allowthe pieces to be advanced in a precise fashion through the productionapparatus.

FIG. 4 illustrates one embodiment of a substrate being fed from left toright through a process in accordance with the present invention.

FIG. 5A shows an embodiment of the processing method wherein twosubstrates are fed and processed simultaneously by a sequentialsputter-evaporate in accordance with the present invention.

FIG. 5B shows a top view of an embodiment of the processing methodwherein two substrates are fed and processed simultaneously by asequential sputter-evaporate/sputter-evaporate process.

FIG. 6 illustrates another embodiment of a process in accordance withthe invention wherein zones further comprise one or more sub-zones.

FIG. 7 shows a schematic of the pallet used in the present inventionpopulated with a plurality of substrate work pieces.

FIG. 8 shows a schematic of a cartridge used to stack a plurality ofsubstrates in a controlled environment.

FIG. 9 shows a schematic production technique employing the cartridgesystem to allow discontinuations in a photovoltaic manufacturingprocess.

DETAILED DESCRIPTION OF THE INVENTION General Photovoltaic Stack Designs

The present invention employs a new production apparatus to producephotovoltaic devices. Of course, the particular apparatus will dependupon the specific photovoltaic device design, which can be varied.However, the base premise is that each photovoltaic device has aphotovoltaic device or thin-film solar cell 100 comprises a substrate105, a barrier layer 110, a back contact layer 120, a semiconductorlayer 130, an alkali materials 140, another semiconductor layer 150, ann-type junction buffer layer 160, an intrinsic transparent oxide layer170, and a transparent conducting oxide layer 180. This stack of layers,according to the present invention, will be made on a plurality ofsubstrates arrayed on a pallet 700, shown in FIG. 7. The individualsubstrate pieces 710 will be arrayed on the pallet, fixed by a fixturemeans.

General Apparatus Configurations

A first embodiment of the invention is an apparatus for manufacturing aphotovoltaic device comprising a means for providing a plurality ofpallets holding multiple substrate pieces, in sequence, to a pluralityof reaction zones. These reaction zones include at least a zone capableof providing an environment for deposition of a semiconductor layer, anda zone capable of providing an environment for depositing a precursorp-type absorber layer.

FIG. 7 shows a schematic top view of a pallet. The pallet provides aholding basis 700 for a plurality of small PV work piece substrates 710,or working substrates fixedly attached to the pallet in a pre-determinedmanner so that the individual work pieces are presented in eachtreatment chamber in a precise and controllable fashion. The palletitself is engineered so that the position of the pallet can be preciselydetermined. The pallet also has a means for allowing attachment to adrive means to advance the pallet through the treatment chamber.Materials of the body of the pallet are chosen so that they arethermally stable and do not interact with the treatment or depositionmaterials used in the reaction or deposition chamber.

Fixturing Means

Furthermore, the means for securing the work pieces to the pallet arereleasable. In some instances the means for affixing the work piece ismagnetic, either because the substrate of the work piece is itselfferro-magnetic, or with an overlay that hold the individual pieces tothe body of the pallet. A mask may be employed to hold each piece wherethere is a frame and a plurality of panes that allow deposition throughsaid pane on the work piece substrates.

FIG. 4 shows as the plurality of pallets are processed through theseries of treatment chambers 420, 430 used to deposit the multiplerequired layers for a photovoltaic device, the train ofreaction/deposition chambers may be fed by loaded cartridges containinga plurality of pallets 440 (see also FIG. 8), and after the desiredlayers are deposited and processed the finished work pieces arecollected in a cartridge 450 and stored for further processing ormanufacturing steps (see also FIG. 9).

In an alternative method, the starting piece cartridge 440 feeds asystem that might provide surface treatment of the substrate, depositionof the junction layer, deposition of the alkali-containing semiconductorsource layer, deposition of a p-type absorber layer, and then formationof the junction and n-type layer, and a buffer so that the worked-onpieces can be taken from the controlled reaction train and inventoriesfor further processing.

Method of Thin Film Manufacturing

One form of the invention provides a method for manufacturing aphotovoltaic device comprising the step of providing a pallet, capableof holding a substrate, in sequence to a plurality of reactor zoneswherein the plurality of zones includes at least one zone depositing aprecursor p-type absorber layer.

In another form, the invention provides a method for manufacturing aphotovoltaic cell comprising the steps of providing a plurality ofsubstrate pieces affixed to a pallet carrier means, depositing aconductive film on the surface of said plurality of substrate pieces,wherein the conductive film includes a plurality of discrete layers ofconductive materials, depositing at least one p-type absorber layer onthe conductive film, wherein the p-type semiconductor absorber layerincludes a metal based alloy material, e.g., alloys of Cu, In, Ga, andpossibly Se or S, and depositing an n-type semiconductor layer on thep-type semiconductor layer forming a p-n junction.

A series of treatment chambers are provided where each chamber providesa specific treatment environment, as well as the means for depositingspecified materials onto the working surface, or interface of the workpieces being processed in order to produce a specific layer depositionor layer treatment. Each of these treatment chambers allow a means totransport the work pieces (marked on the pallet being made into thephotovoltaic device) to be transported from the first designed chamber,through the sequential plurality of chambers, until the work piece hasbeen made into the designed photovoltaic stack.

This plurality of reaction or treatment chambers provided with atransport mechanism may also include one or more isolation chambers thatensure effective reactants are maintained in specifically desiredchambers and do not contaminate downstream processes. This isolationsystem is particularly important in the formation of the semiconductorlayers of the photovoltaic device, where relatively small amounts ofmaterial determine whether a layer is a p-type or n-type semiconductor.This carrier may be configured with referencing means to ensure the workpieces are positioned within the production apparatus at definedpositions.

FIG. 3 shows a plurality of work piece substrates 310 on a devicecapable of affixing the substrates onto a carrier 320, that also hasmeans that allow the pieces to be advanced in a precise fashion throughthe production apparatus. These pallets are generally flat and havemeans for holding a plurality of work pieces on a surface of the palletso as to present each of the work piece surfaces to a deposition sourceor treatment source.

General Photovoltaic Stack Designs

The present invention employs a new production apparatus to producephotovoltaic devices. Of course, the particular apparatus will dependupon the specific photovoltaic device design, which can be varied.

Viewing FIG. 1, all layers are deposited on a substrate 105 which maycomprise one of a plurality of functional materials, for example, glass,metal, ceramic, or plastic. Deposited directly on the substrate 105 is abarrier layer 110. The barrier layer 110 comprises a thin conductor orvery thin insulating material and serves to block the out diffusion ofundesirable elements or compounds from the substrate to the rest of thecell. This barrier layer 110 may comprise chromium, titanium, siliconoxide, titanium nitride and related materials that have the requisiteconductivity and durability. The next deposited layer is the backcontact layer 120 comprising non-reactive metals such as molybdenum. Thenext layer is deposited upon the back contact layer 120 and is a p-typesemiconductor layer 130 to improve adhesion between an absorber layerand the back contact layer. The p-type semiconductor layer 130 may be aI-III_(a,b)-VI isotype semiconductor, but the preferred composition isCu:Ga:Se; Cu:Al:Se or Cu:In:Se alloyed with either of the previouscompounds.

In this embodiment, the formation of a p-type absorber layer involvesthe interdiffusion of a number of discrete layers. Ultimately, as seenin FIG. 1, the p-type semiconductor layers 130 and 150 combine into asingle composite layer 155 which serves as the prime absorber of solarenergy. In this embodiment, however, alkali materials 140 are added forthe purpose of seeding the growth of subsequent layers as well asincreasing the carrier concentration and grain size of the absorberlayer 155, thereby increasing the conversion efficiency of the solarcell. The layers are then thermally treated at a temperature of about400° C.-600° C.

After the thermal treatment, the photovoltaic production process iscontinued by the deposition of an n-type junction buffer layer 160. Thislayer 160 will ultimately interact with the absorber layer 155 to formthe necessary p-n junction 165. A transparent intrinsic oxide layer 170is deposited next to serve as a hetero-junction with the CIGS absorber.Finally, a conducting transparent oxide layer 180 is deposited tofunction as the top of the electrode of the cell. This final layer isconductive and may carry current to a grid carrier that allows thecurrent generated to be carried away.

Alternative Pallet Based Manufacturing Schemes

FIG. 2 schematically represents a reactor 200 for forming solar cells. Asubstrate 205 is fed left to right through the reactor. The reactor 200includes one or more processing zones, referred to in FIG. 2 as 220,230, 240 and 250, wherein each processing zone comprises an environmentfor depositing materials on a substrate 205. The zones are mechanicallyor operatively linked together within the reactor 200. As used herein,the term environment refers to a profile of conditions for depositing orreacting a material layer or mixture of materials on the substrate 205while the substrate 205 is in a particular zone.

Each zone is configured according to which layer of the solar cell isbeing processed. For example, a zone may be configured to perform asputtering operation, including heat sources and one or more sourcetargets.

Preferably, an elongated substrate 205 is passed through the variousprocessing zones at a controllable rate. It is further contemplated thatthe substrate 205 may have a translational speed of 0.5 m/min to about 2m/min. Accordingly, the process internal to each of the zones ispreferably tuned to form the desired cross-section given the residencetime the material is proximate to a particular source material, giventhe desired transport speed. Thus, the characteristics of each process,such as material and process choice, temperature, pressure, orsputtering delivery rate, etc., may be chosen to insure that constituentmaterials are properly delivered given the stack's residence time asdetermined by the transport or translation speed.

According to the invention, the substrate 205 may be transportedcontinually through the process in a palletized fashion in a “pictureframe” type mount for indexing and transportation through the process,the latter of which is illustrated in FIG. 3. Referring to FIG. 3 onesubstrate or group of substrates 310 are mounted on a pallet 320 thattranslates through one or more zones 330 and 340 on track 350. Inalternate embodiments the process may further comprise a secondsubstrate or set of substrates placed in a back to back configurationwith substrate 310.

It is contemplated that the background pressure within the various zoneswill range from 10⁻⁶ torr to 10⁻³ torr. Pressures above base-vacuum(10⁻⁶ torr) may be achieved by the addition of a pure gas such as Argon,Nitrogen or Oxygen. Preferably, the rate R is constant resulting in thesubstrate 205 passing through the reactor 200 from entrance to exitwithout stopping. It will be appreciated by those of ordinary skill inthe art that a solar cell stack may thus be formed in a continuousfashion on the substrate 205, without the need for the substrate 205 toever stop within the reactor 200.

The reactor in FIG. 2 may further comprise vacuum isolation sub-zones orslit valves configured to isolate adjacent process zones. The vacuumisolation sub-zones or slit valves are provided to facilitate thecontinuous transport of the substrate between different pressureenvironments.

The reactor shown in FIG. 2 is a plurality of N-processing zones 220,230, 240 and 250. However, it should be recognized by one skilled in theart that the reactor may comprise zones 220, 230, 240, 250 . . . Nzones. The load/unload zones 210/211 comprise zones that can be isolatedfrom the rest of the reactor and can be open to atmosphere.

In a preferred embodiment, the process may further comprise a substrate206 that runs back-to-back with substrate 205. In this embodimentsubstrates 206 and 205 are oriented in a back-to-back configuration andrun through zones 220, 230, 240, and 250 performing identical processoperations 222/221, 232/231, 242/241 and 252/251.

FIG. 5A shows a top illustration of a portion of a reactor 500processing substrates 501 and 502 in a back-to-back fashion and alsoillustrates a sequential sputter-evaporate process isolated by zone 511.To achieve back-to-back processing, heat sources 503 for substrate 501are mirrored as heat sources 507 for substrate 502. Likewise, sputteringsource 504, heat sources 505, and evaporative sources 506 for substrate501 are mirrored for substrate 502 as sputtering source 508, heatsources 509, and evaporative sources 510.

FIG. 5B shows a top illustration of a portion of a reactor 512processing substrates 521 and 522 in a back-to-back fashion with asequential sputter-evaporate/sputter-evaporate process. As in FIG, 5A,sputter sources 534 for substrate 521 are mirrored as sputter sources528 for substrate 522. Likewise, heat sources 523 and 526, evaporativesources 524 and 527, and sputtering source 525 for substrate 521 aremirrored for substrate 522 as heat sources 529 and 532, evaporativesources 530 and 533, and sputtering source 531. Hence, with the simpleduplication of heat and material sources, solar cell production may beeffectively doubled within the same machine.

Specific Processing Steps

Of course, the method steps for producing a particular PV articledepends upon the specific design of that article. CIGS based PVs willhave a different production method than Si based systems. The presentinvention is not so limited to one PV type and in general any PV couldbe made with the technology of the invention.

In cases of CIGS, the specific steps might include: loading a palletbased substrate through an isolated loading zone or like unit 210. Invarious embodiments, the isolation zone 210 is contained within thereactor 200. Alternatively, the isolation zone 210 may be attached tothe outer portion of the reactor 200. The first processing zone 210 mayfurther comprise a substrate preparation environment to remove anyresidual imperfections at the atomic level of the surface. The substratepreparation may include: ion beam, deposition, heating, orsputter-etching. These methods are known in the art and will not bediscussed further.

A second processing zone may be an environment for depositing a barrierlayer for substrate impurity isolation, wherein the barrier layerprovides an electrically conductive path between the substrate andsubsequent layers. In a preferred embodiment, the barrier layercomprises an element such as chromium or titanium delivered by asputtering process. Preferably, the environment comprises a pressure inthe range of about 10⁻⁶ torr to about 10⁻² torr at ambient temperature.

A third processing zone downstream from the previous zones comprises anenvironment for the deposition of a metallic layer to serve as a backcontact layer. The back contact layer comprises a thickness thatprovides a conductive path for electrical current. In addition, the backcontact layer serves as the first conducting layer of the solar cellstack. The layer may further serve to prevent the diffusion of chemicalcompounds such as impurities from the substrate to the remainder of thesolar cell structure or as a thermal expansion buffer between thesubstrate layer and the remainder of the solar cell structure.Preferably, the back contact layer comprises molybdenum, however, theback contact layer may comprise other conductive metals such asaluminum, copper or silver.

A fourth zone provides an environment for deposition of a p-typesemiconductor layer. As used herein, this layer may serve as anepitaxial template for absorber growth. Preferably, the p-typesemiconductor layer is an isotype I-IIIVI₂ material, wherein the opticalband gap of this material is higher than the average optical band gap ofthe p-type absorber layer. For example, a semiconductor layer maycomprise Cu:Ga:Se; Cu:AI:Se or alloys of Cu:In:Se with either of theprevious compounds. Preferably, the materials are delivered by asputtering process at a background pressure of 10⁻⁶ to 10⁻² torr and attemperatures ranging from ambient up to about 300° C. More preferably,temperatures range from ambient to about 200° C.

A fifth zone, downstream from the previous zones, provides anenvironment for the deposition of alkali materials to enhance the growthand the electrical performance of a p-type absorber. Preferably, thealkali materials are sputtered, at ambient temperature and a pressurerange of about 10⁻⁶ torr to 10⁻² torr. Preferably, the materialcomprises NaF, Na₂Se, Na₂S or KCl or like compounds wherein thethickness ranges from about 150 nm to about 500 nm.

A sixth zone, also downstream from the previous zones, may comprise anenvironment for the deposition of another semiconductor layer comprisingp-type absorber precursor materials. In a preferred embodiment, thesixth zone may further comprise one or more sub-zones for the depositionof the precursor materials. In one embodiment, the semiconductor layeris formed by first delivering precursor materials in one or morecontiguous sub-zones, then reacting the precursor materials into thefinal p-type absorber in a downstream thermal treatment zone. Thus,especially for CIGS Systems, there may be two material deposition stepsand a third thermal treatment step in the format of the layer.

In the precursor delivery zones, the layer of precursor materials isdeposited in a wide variety of ways, including evaporation, sputtering,and chemical vapor deposition or combinations thereof preferably, theprecursor material may be delivered at temperatures ranging from about200° C.-300° C. It is desired that the precursor materials react to formthe p-type absorber as rapidly as possible. As previously discussed, tothis end, the precursor layer or layers may be formed as a mixture or aseries of thin layers.

A manufacturing device may also have seventh processing zone downstreamfrom previous processing zones for the thermal treatment of one or moreof the previous layers. The term multinaries includes binaries,ternaries, and the like. Preferably, thermal treatment reacts previouslyunreacted elements or multinaries. For example, in one embodiment it ispreferred to have Cu, In, Se, and Ga in various combinations and ratiosof multinary compounds of elements as the source for deposition on thework piece. The reactive environment includes selenium and sulfur invarying proportions and ranges in temperature from about 400° C. toabout 600° C. with or without a background inert gas environment. Invarious embodiments, processing time may be minimized to one minute orless by optimizing mixing of the precursors. Optimal pressures withinthe environment depend on whether the environment is reactive or inert.According to the invention, within the thermal treatment zone, thepressures range from about 10⁻⁵ to about 10⁻² torr. However, it shouldbe noted that these ranges depend very much on the reactor design forthe stage, the designer of the photovoltaic device and the operationalvariables of the apparatus as a whole.

The reactor may have an eighth processing zone for the formation of ann-type semiconductor layer or junction partner. The junction layer isselected from the family II-VI, or IIIx VI. For example, the junctionlayer may comprise ZnO, ZnSe, ZnS, In, Se or In_(N)S deposited byevaporation, sublimation or chemical vapor deposition methodologies. Thetemperatures range from about 200° C. to about 400° C.

Additionally, the process may also have a ninth zone having anenvironment for deposition of an intrinsic layer of a transparent oxide,for example ZnO. According to the invention, the intrinsic transparentoxide layer may be deposited by a variety of methods including forexample, RF sputtering, CVD or MOCVD.

In various embodiments, the process further has a tenth zone with anenvironment for the deposition of a transparent conductive oxide layerto serve as the top electrode for the solar cell. In one embodiment forexample, aluminum doped ZnO is sputter deposited. Preferably, theenvironment comprises a temperature of about 200° C. and a pressure ofabout 5 millitorr. Alternatively, ITO (Indium Tin Oxide) or similar maybe used.

In one embodiment, as described above, the reactor may comprise discretezones wherein each zone corresponds to one layer of photovoltaic deviceformation. In a preferred embodiment however, zones comprising similarconstituents and or environment conditions may be combined therebyreducing the total number of zones in the reactor.

For example, in FIG. 6, zone 610 comprises sub-zones 611 and 612, zone615 comprises sub-zones 616 and 617, and zone 620 comprises one zone,wherein each zone and sub-zone comprises a predetermined environment. Inthis example, a material A may be deposited in sub-zone 611 and adifferent material B may be deposited in sub-zone 612, wherein theenvironment of sub-zone 612 downstream from material A differs from theenvironment in sub-zone 611. Thus, the substrate 605 may be subjected toa different temperature or other process profiles while in differentregions of the same zone 610. According to this embodiment, the zone maybe defined as having a predetermined pressure, and a zone may includeone or more regions, sub-zones, or phases therein, with each sub-zoneconfigured to deposit or react a desired material or materials withinthe same pressure environment.

The substrate 605 may then be passed to chamber 615, where material C isdeposited within sub-zone 616, and material D is deposited in sub-zone617. Finally, the substrate 605 reaches a zone 620, where a singlematerial E is deposited.

As will be appreciated by those of ordinary skill in the art, thereactor 600 may be described as having a series of zones disposedbetween the entrance and exit of the reactor along a path defined by thetranslation of the substrate. Within each zone, one or more constituentenvironments or sub-zones may be provided to deposit or react a selectedtarget material or materials, resulting in a continuous process forforming a solar cell stack. Once the substrate enters the reactor, thevarious layers of a solar stack are deposited and formed in a sequentialfashion, with each downstream process in succession contributing to theformation of the solar cell stack until a finished thin film solar cellis presented at the exit of the reactor.

While the present technique has been couched in terms of CIGS basedphotovoltaic stack designs, it must be understood that the technique mayalso be employed for the production of other photovoltaic designsincluding production of silicon based systems such as those discussed instate of the art. For instance, it would be possible to use or includecarbon or germanium atoms in hydrogenated amorphous silicon alloys inorder to adjust their optical bandgap. For example, carbon has a largerbandgap than silicon and thus inclusion of carbon in a hydrogenatedamorphous silicon alloy increases the alloy's bandgap. Conversely,germanium has a smaller bandgap than silicon and thus inclusion ofgermanium in a hydrogenated amorphous silicon alloy decreases thealloy's bandgap.

Similarly one could incorporate boron or phosphorus atoms inhydrogenated amorphous silicon alloys in order to adjust theirconductive properties. Including boron in a hydrogenated amorphoussilicon alloy creates a positively doped conductive region. Conversely,including phosphorus in a hydrogenated amorphous silicon alloy creates anegatively doped conductive region.

Hydrogenated amorphous silicon alloy films are prepared by deposition ina deposition chamber. Heretofore, in preparing hydrogenated amorphoussilicon alloys by deposition in a deposition chamber, carbon, germanium,boron or phosphorus have been incorporated into the alloys by includingin the deposition gas mixture carbon, germanium, boron or phosphoruscontaining gases such as methane (CH₄), germane (GeH₄), germaniumtetrafluoride (GeF₄), higher order germanes such as digermane (Ge₂ H₆),diborane (B₂ H₆) or phosphine (PH₃). See for example, U.S. Pat. Nos.4,491,626, 4,142,195, 4,363,828, 4,504,518, 4,344,984, 4,435,445, and4,394,400. A drawback of this practice, however, is that the way inwhich the carbon, germanium, boron or phosphorus atoms are incorporatedinto the hydrogenated amorphous silicon alloy is not controlled. Thatis, these elements are incorporated into the resulting alloy in a highlyrandom manner thereby increasing the likelihood of undesirable chemicalbonds.

Thus, in cases where PV devices are manufactured, and specific andcontrolled reaction and or deposition conditions are required to producethe films of the PV, the present invention technology will be useful.

1. An apparatus for manufacturing a photovoltaic device comprising ameans for providing a plurality of pallets holding multiple substratepieces in sequence to a plurality of reaction zones including at least:a zone capable of providing an environment for deposition of asemiconductor layer; and a zone capable of providing an environment fordepositing a p-type absorber layer.
 2. The apparatus for manufacturing aphotovoltaic device of claim 1 further comprising a means for providingin sequence a substrate to a plurality of reactor zones for preparingsaid substrate.
 3. The apparatus for manufacturing a photovoltaic deviceof claim 1 further comprising a first processing zone capable ofproviding an environment for transition of the substrate from an ambientenvironment to the processing environment.
 4. The apparatus of claim 3wherein the substrate transitions, in part or whole, from atmosphericpressure to reduced pressure consistent with the subsequent processingenvironment.
 5. The apparatus for manufacturing a photovoltaic device ofclaim 1 further comprising a processing zone capable of providing anenvironment for deposition of a barrier layer.
 6. The apparatus of claim5 wherein the barrier layer comprises a thin conductor or very thininsulating material.
 7. The apparatus for manufacturing a photovoltaicdevice of claim 1 further comprising a processing zone capable ofproviding an environment for deposition of a conductive back contactlayer.
 8. The apparatus of claim 7 wherein the deposition of aconductive back contact layer comprises a metallic layer.
 9. Theapparatus of claim 8 wherein the metallic layer is comprise conductivemetals chosen from the group consisting of molybdenum, titanium,tantalum, or other acceptable metals or alloys.
 10. The apparatus ofclaim 9 wherein the metallic layer is molybdenum.
 11. The apparatus formanufacturing a photovoltaic device of claim 1 further comprising aprocessing zone capable of providing an environment for deposition ofalkali materials.
 12. The apparatus of claim 11 wherein the alkalimaterials are Na-VII or Na₂-VII.
 13. The apparatus for manufacturing aphotovoltaic device of claim 1 further comprising a processing zonecapable of providing an environment for deposition of a semiconductorlayer.
 14. The apparatus of claim 13 wherein the semiconductor layercomprises Group I, III, VI elements.
 15. The apparatus of claim 14wherein the semiconductor layer comprises CuGaSe₂, CuAlSe₂, or CuInSe₂alloyed with one or more of the I, III, VI elements.
 16. The apparatusof claim 15 wherein the semiconductor layer comprises CuGaSe₂.
 17. Theapparatus for manufacturing a photovoltaic device of claim 1 furthercomprising a processing zone capable of providing an environment fordeposition of a semiconductor layer wherein the layer comprisesprecursor materials.
 18. The apparatus of claim 17 wherein the precursormaterials comprise Group I, III, VI elements.
 19. The apparatus of claim18 wherein the precursor materials comprise a I-(IIIa,IIIb)-VI₂ layer.20. The apparatus of claim 19 wherein the precursor materials compriseone or more of the elements of a I-(IIIa,IIIb)-VI₂ layer where the0.0<IIIb/(IIIa+IIIb)<0.4.
 21. The apparatus of claim 19 wherein theprecursor materials comprise one or more of the alloys of aI-(IIIa,IIIb)-VI₂ layer where the 0.0<IIIb/(IIIa+IIIb)<0.4.
 22. Theapparatus of claim 19 wherein the semiconductor layer comprises a CIGSabsorber layer comprising In_(1-x):Ga_(x):Se₂ where x ranges between 0.2to 0.3 wherein the thickness ranges from about 1 μm to about 3 μm. 23.The apparatus of claim 22 where the CIGS absorber layer is formed by thedelivery of type I, III and VI precursor metals where Cu, In_(1-x),Ga_(x), and Se₂ layers are sequentially deposited on the substrate. 24.The apparatus of claim 22 where the CIGS absorber layer is formed by thedelivery of the type I, III and VI precursor metals where Cu, In_(1-x),Ga_(x), and Se₂ layers are sequentially deposited on the substrate andthen synthesized into an alloy mixture with a thermal treatment.
 25. Theapparatus of claim 22 where the CIGS absorber layer is formed by thedelivery of type I, III and VI precursor metals where an Cu:Ga_(x) layeris separately synthesized, and then co-deposited with an In_(x-1) layerand Se₂ layer on a substrate.
 26. The apparatus of claim 22 where theCIGS absorber layer is formed by the delivery of type I, III and VIprecursor metals where a Cu:Ga_(x) layer is separately synthesized, andthen co-deposited with an In_(1-x) layer and Se₂ layer on a substrate;and then synthesized into an alloy mixture with a thermal treatment. 27.The apparatus of claim 22 where the CIGS absorber layer is formed by thedelivery of type I, III and VI precursor metals where anCu:Ga_(x):In_(x-1) layer is separately synthesized, and thenco-deposited with an Se₂ layer on a substrate.
 28. The apparatus ofclaim 22 where the CIGS absorber layer is formed by the delivery of typeI, III and VI precursor metals where a Cu:Ga_(x):In_(x-1) layer isseparately synthesized, and then co-deposited with an Se₂ layer on asubstrate; and then synthesized into an alloy mixture with a thermaltreatment.
 29. The apparatus for manufacturing a photovoltaic device ofclaim 1 further comprising a processing zone capable of providing anenvironment for thermal treatment of one or more layers.
 30. Theapparatus of claim 29 wherein the treatment occurs in the pressure rangeof 10⁻⁶ torr up to atmospheric pressure and temperature range of 300° C.to 700° C.
 31. The apparatus for manufacturing a photovoltaic device ofclaim 1 further comprising a processing zone capable of providing anenvironment for deposition of an n-type semiconductor layer.
 32. Theapparatus of claim 31 wherein the n-type semiconductor layer isdiscrete.
 33. The apparatus of claim 32 wherein the discrete layercomprises one or more of Group II-VI, III-VI elements.
 34. The apparatusof claim 32 wherein the discrete layer materials comprise one or more ofthe following groups (In,Ga)_(y)(Se,S,O) and (Zn,Cd) (Se,S,O).
 35. Theapparatus of claim 32 wherein the discrete layer materials comprise oneor more of the following materials chosen from the group consisting of(In,Ga)₂Se₃, (In,Ga)₂S₃, ZnSe, ZnS, and ZnO.
 36. The apparatus of claim32 wherein the n-type semiconductor layer is formed by diffusion of adopant species into the p-type absorber layer.
 37. The apparatus ofclaim 36 wherein the dopant species is chosen from the group consistingof one or more Group II or III elements.
 38. The apparatus of claim 37wherein the dopant species comprises either Zn or Cd.
 39. The apparatusfor manufacturing a photovoltaic device of claim 1 further comprising aprocessing zone capable of providing an environment for deposition of aninsulating transparent oxide layer.
 40. The apparatus of claim 39wherein the insulating transparent oxide layer comprises one or morematerials from Group II-VI or II-IV-VI.
 41. The apparatus of claim 39wherein the insulating transparent oxide layer comprises one or morematerials ZnO or ITO.
 42. The apparatus for manufacturing a photovoltaicdevice of claim 1 further comprising a processing zone capable ofproviding an environment for deposition of a conducting transparentlayer.
 43. The apparatus of claim 42 wherein the conducting transparentlayer comprises one or more materials from Group II-VI or II-IV-VI. 44.The apparatus of claim 42 wherein the conducting transparent layercomprises one or more materials ZnO, Cd₂SnO₄ or ITO.
 45. The apparatusfor manufacturing a photovoltaic device of claim 1 further comprising afirst processing zone capable of providing an environment for transitionof the substrate from the processing environment back to the ambientenvironment.
 46. The apparatus of claim 45 wherein the substratetransitions, in part or whole, from atmospheric pressure to the reducedpressure consistent with the subsequent processing environment.
 47. Amethod for manufacturing a photovoltaic device comprising providing apallet, capable of holding a substrate, in sequence to a plurality ofreactor zones wherein said plurality of zones includes at least one zonecapable of providing an environment for depositing a p-type absorberlayer.
 48. A method for manufacturing a photovoltaic cell comprising: a.providing a plurality of substrate pieces affixed to a pallet carriermeans; b. depositing a conductive film on the surface of said pluralityof substrate pieces; c. wherein the conductive film includes a pluralityof discrete layers of conductive materials; d. depositing at least onep-type semiconductor layer on the conductive film, wherein the p-typesemiconductor layer includes a copper indium diselenide based alloymaterial; e. depositing an n-type semiconductor layer on the p-typeabsorber layer forming a p-n junction.
 49. A pallet system forproduction of photovoltaic devices comprising: a. a pallet base with afirst side and a second side where disposed on said first side of saidpallet base is a plurality of regularly disposed target areas; whereineach of said plurality of disposed target areas has means for fixing awork substrate in a removable fashion; b. indexing means disposed onsaid pallet base allowing control of the positioning of said palletbase; c. fixing means is magnetic means; d. magnetic means have thermalreservoir capacity disposed evenly over said designated target areas; e.work substrate is a magnetic material such as stainless steel; f.fixable means is mechanical.
 50. A pallet system for production ofphotovoltaic devices comprising: a. a pallet base with a first side anda second side where said first side has a plurality of regularlydisposed target areas disposed on said first side of said pallet base;b. a plurality of regularly disposed target areas disposed on saidsecond side of said pallet base; wherein each of said plurality ofdisposed target areas has means for fixing a work substrate in aremovable fashion; c. indexing means disposed on said pallet baseallowing control of the positioning of said pallet base.